Historically, innovations in lateritic-based nickel production are chiefly the outcome of technologies initially used in uranium processing, and later applied to the gold and copper industries. A good case in point is extraction by solvent (SX) and ionic exchange resins (IX). Using pyrometallurgy and hydrometallurgy, four processes are currently assessed and used in the nickel industry. Current process technologies basically differ in their initial stage.
In lateritic ore processing, there are many options available. However, selecting the best process for a plant initially depends on the ore available. Chemical or thermal treatment is used in lateritic nickel deposits processing. Plants using reduction furnaces or acid leaching have faced many challenges in engineering, construction, start-up, and operational development. A wide-ranging variety of flowcharts can be used for profiting nickel lateritic ores involving pyrometallurgical and hydrometallurgical processes. Chemical composition of lateritic ores varies widely from deposit to deposit, and this variation certainly defines the best process route to be used.
Pyrometallurgical Process—Fusion In pyrometallurgical processes, special mention goes to fusion (melting) for FeNi production, adequate for ores mostly containing saprolite (garnierite supergenic enrichment). These ores contain proportionately low levels of cobalt and iron, compared to limonitic ores. The Ni/Co and Ni/Cu ratios to feed the FeNi process must be above 40 and 80, respectively. The pyro fusion process can yield FeNi or matte. Ore preparation stage comprises drying, calcination and, at times, reduction in rotary furnace or casting in electric furnace in the presence of reducing sources. If matte is the product to be produced, then elementary sulfur is added to the furnace. Pyrometallurgical processes are intensive energy consumers and, thus, all humidity and water combined must be removed from the process. Fusion of the mix can reach temperatures in the 1400° to 1600° C. range. Electric power and fuel as reducing agents are the two costliest items in the process. Fusion temperature is mainly a function of the SiO2/MgO ratio and the FeO grade. In an electric furnace, the temperature difference of metal or matte and slag can vary between 100° and 200° C. This process demands that the SiO2/MgO ratio be between 1.8 and 2.0.
In addition to the fusion (melting) pyrometallurgical process, Caron (reduction process/ammonia leaching) and HPAL (high pressure acid leaching) are currently the two hydrometallurgical processes to recover nickel and cobalt in laterites. These technologies require a relative aggressive chemical treatment and high capital investment, in addition to a strong dependency on the cost of fuel and sulfuric acid/sulfur, respectively.
Caron Process—Caron is a process normally used in lateritic ores comprising a mix of limonite and saprolite. The ore is dried and the nickel is selectively reduced (with cobalt and partly iron) to metal at temperatures around 700° C. Subsequently, basic metals are selectively extracted via leaching through an ammonia solution. This Caron process is industrially used in four plants: Nicaro and Punta-Gorda in Cuba, Niquel Tocantins in Brazil and Yabulu in Australia. This process has several downsides: ore preparation involves drying, calcination and reduction, which are heavy consumers of energy. The leaching stage uses ammonia, whose odor is highly unpleasant. Nickel recovery rate falls short of the fusion (melting) and HPAL processes.
HPAL Process—The ore fraction used in the HPAL process is predominantly limonitic. A small portion of saprolitic ore can also be mixed, provided that Mg and Al grades do not excessively raise sulfuric acid consumption. This reagent is roughly 30% of nickel operating cost. Leaching is carried out in autoclaves at temperatures in the 145 to 270° C. range. Products from an HPAL plant can be: electrolytic nickel, nickel oxide, or nickel briquettes. Some industrial plants produce intermediate products, such as mixed sulfide or a hydroxide mix of nickel and cobalt.
Acid leaching is a process mostly developed in Australia. As the sulfur price declined, an opportunity arose to reconsider further use of lateritic ores with other features, which were not used in traditional production processes. Furthermore, nickel was recovered with greater purity, efficiency and reduction of operating costs. Other incipient modalities of acid leaching under atmospheric conditions are part of new technologies to extract nickel and cobalt from ores, such as sulfuric or chloride leaching.
Flexibility, low capital cost, high metal recovery, low operating cost, and energy generation all translate into a logistics which could indicate the atmospheric leaching technology as the process of choice in medium-term and long-term development of lateritic deposits. Many analysts believe that operating costs can be reduced, as can investments (cost of capital/year).
Several atmospheric leaching hydrometallurgical routes are being developed to extract nickel and cobalt from lateritic ores such as those described in US 2005/0226797 A1 “Atmospheric Pressure Leach Process for Lateritic Nickel Ore” to H. Liu, et al. and WO 06/000098 “Method for Nickel and Cobalt Recovery from Laterite Ores by Reaction with Concentrated Acid and Water Leaching” to D. Neudorf. The objective in these routes is to render metals soluble, using inorganic acids, followed by solid-liquid separation and neutralization, prior to final metal recovery. Selective recovery of the metal present in the leaching pulp is a major item in economic evaluation. Presence of many impurities (such as copper, iron, magnesium and others) may well be the top technological hurdle to be overcome. One option may be the use of physical-chemical methods, such as using ionic exchange materials and extraction via solvents. In the specific case of nickel and cobalt, which is the purpose of the present invention, it worth noting that they have very similar chemical properties. This facilitates their mutual recovery, whether through precipitation as sulfides or extraction via solvents in a chloride, ammonia or sulfur medium. As for ionic exchange, further detailed in the present invention, studies are being intensified and various approaches have yielded rather promising results.
Atmospheric sulfuric leaching can be used in some types of lateritic ores with low iron grade, leading to significant reduction in investments. This involves vat leaching at temperatures below boiling point. Normally, some reducing agent is added, to control Eh in the 800-900 mV range. Results are promising, with slight decrease in nickel ore, if compared to the HPAL process, even though there is greater sulfuric acid consumption.
Characteristics of Sulfuric Atmospheric Leaching
                Applicable to lateritic ores—limonitic and saprolitic fractions undergo atmospheric pressure treatment        Simplicity in operation, process control and maintenance        No exotic construction materials (Ti) are used        High availability with no unplanned depressurizing        Highly attractive in terms of investment and operating cost        No industrial application        
Chloride atmospheric leaching occurs under atmospheric pressure and temperatures below the boiling point, with HCl recovery as shown in the processes below. This process is being considered by Jaguar Nickel for the Ceceou deposit in Guatemala. Major upsides are lower investment cost vis-à-vis the HPAL process and recycling the HCl leaching agent through pyrohydrolysis regeneration. Its downside is the use of special materials resistant to high temperatures in a chloride acid environment.
Characteristics of Chloride Atmospheric Leaching
                Treating ores with grades up to 25% of Mg        High Ni and Co extraction rates (95%)        HCl production via H2SO4 (which is five times less expensive, with high reaction power)        A simple process        No difficult wastes are generated for later disposal        Potential income from byproducts, such as Mg and Fe as chloride, but mainly as Glauber salt (Na2SO4.10H2O)        Possible treatment of ore's more acid fraction (Magnetic—High Fe-Low Mg) and its less acid fraction (Non-magnetic—Low Fe-High Mg) in two different flows less acid consumption, shorter residence time.        No use of exotic materials such as Ti in the equipments. Coal is used as chlorination energy source.        Several upsides (lower operating cost, lower capital cost, possible acid regeneration, engineering modernization, downstream inclusion with greater simplicity and savings, searching for metal with adequate London Metal Exchange [LME] grade) make these new technologies ever more feasible and attractive in nickel ore processing. Flexibility, low capital cost, high metal recovery, low operating cost, and energy generation all translate into a logistics which can indicate the atmospheric leaching technology as the process of choice in medium-run and long-run development of lateritic deposits.        
All acid leaching plants include a multi-stage circuit for settlement in countercurrent, for solid-liquid separation. This demands considerable capital & operating costs, uses large areas and requires significant amounts of washing water. An alternative to recover nickel and cobalt from the leaching pulp without using thickeners is to use a resin-in-leach (RIL) system, which is the objective of the present invention. The last decade has seen plenty of ionic exchange resin in hydrometallurgical processes, driven mainly by the activated coal technology in gold mining. Moreover, ionic exchange resins are commercially available for nearly any separation process. Its use can ensure more effective and simple purification, if compared to purification by precipitation or extraction through solvent—the two most commonly used method for this purpose. An adsorption or ionic exchange process is more adequate and satisfactory to recover or remove low concentration of some metal ions in the presence of an excess of other metals. Furthermore, ionic exchange needs no costly filtration, no low selectivity of nickel or other metals, there is no reagent loss—all of which are disadvantages inherent to extraction-by-solvent processes.
The acid leaching process generates an acid pulp containing dissolved metals, including high concentrations of iron, aluminum, manganese and magnesium, in addition to nickel, cobalt and copper. Some upsides influence the decision to use the ionic exchange resin technology in hydrometallurgical extraction processes. These considerations are: (1) lesser environmental impact—less water consumption and opportunity for water recycling; (2) lower operating & capital cost; and (3) higher quality of metal products—high selectivity for metals of interest and high separation capacity. The RIL technology can be used to replace conventional counter current decantation (CCD) technology, in order to reduce cost and environmental impact
Every nickel lateritic ore leaching process includes a multi-stage settlement circuit in CCD, followed by precipitation and/or liquid-solid extraction for metal recovery. When a low grade nickel lateritic ore is hydrometallurgically treated and liquid-solid separation becomes necessary, the operating cost is significant, process inefficiency causes nickel loss, due to the difficulty in washing solids and in recovering the dissolved species. A solution to this constrain is to recover the dissolved metal in the pulp itself, during leaching, using an ionic exchanger and rendering the liquid-solid separation unnecessary. An alternative to recover nickel and cobalt while the pulp is being leached would be to use the resin-in-leach system, which is the purpose of the present invention. This technology—industrially proven in gold and uranium recovery—can be used in processes which contemplate replacing conventional CCD technology. Using the ionic exchange technique with polymeric resins should offer some advantages, such as (1) no reagent losses due to dragging, as is the case in other extraction-by-solvents processes, and (2) efficient recovery and removal of minor concentrations of some metal ions or an excess of other metals. The ionic exchange resin technique tends to lower operating & capital costs, to ensure greater sustainability without using organic products, such as in extraction through solvents.
A RIL process can be used, through resin adsorption, in recovering metals dissolved during leaching, but prior to pulp solid-liquid separation, thus avoiding product loss. Ionic-exchange polymeric resins have been increasingly used in the last decade, and have been commercially available for nearly all separation processes. The process is free from reagent loss and the resins promote more effective and direct purification, if compared to purification via precipitation or extraction by solvents—which are commonly-used techniques. The RIL process of the invention used in nickel recovery due to acid leaching provide the following benefits:    a) Acid leaching can produce a hard-to-settle pulp or solids which, when separated, are difficult to wash. The RIL process solve these operating hurdles by eliminating the solid-liquid separation stage;    b) Reduced investment cost, due to use of ionic exchange resins in the same equipment circuit during leaching and adsorption;    c) Nickel loss is minimized through co-precipitation, since pulp neutralization can be eliminated or dampened. The resin added to the pulp has more adsorption kinetics, allowing nickel to be loaded as soon as it is leached, long before coprecipitation during the neutralization process;    d) Preferential and kinetic nickel adsorption is swifter than in other soluble metals, because nickel is immediately captured by the resin as soon as it is dissolved;    e) Greater nickel and cobalt extraction from ore during leaching. Hence, the process provides higher selectivity and higher loading capacity for nickel species in solution. If the dissolved ions are promptly removed from the solution by the ionic exchange mechanism, balance is displaced, as per Lê Chatelier's Law.
The use of ionic exchange resins to recover nickel from acid solutions has been the focus of much research in the last few years. Those skilled in the art believed that resins could not compete with other purification techniques, because resins then produced had low selectivity and—even more importantly—had low mechanical and thermal resistance. However, progress in the last few years has improved such properties considerably. It can be now stated that current resins are quite competitive, if compared to processes of precipitation, crystallization, extraction by solvents, used in impure nickel solutions. Nickel soluble ionic species are adsorbed into resins through an ionic exchange reaction. Resins are synthetic materials with an inert matrix (usually polystyrene cross-linked with divinylbenzene) and functional surface groups. There are basically two types of resins to adsorb nickel from acid solutions: resins with iminodiacetic acid as a functional group, and resins with bis-picolylamine as a functional group. The first resins have a weak acid group and can only exchange ions after pH adjustment. This makes its use difficult, given the need for previous neutralization. Hence, efforts are being made to incorporate resins with the bis-picolylamine group and make them commercially available in the market.
Ionic exchange resin is an innovative nickel-recovery technology, albeit its use in nickel recovery is still under development in the hydrometauurgy area. Its chief rationale for being still incipient is an abundance and efficiency of other purification techniques, such as precipitation and extraction via solvents. Polymeric resins are used to adsorb nickel and cobalt through ionic exchange. Resins are regarded as relatively expensive and their feasible use is limited to RIP (resin in pulp) and RIL techniques, wherein polymeric resins are directly applied to the pulp, with no need for solid-liquid separation. It is interesting to distinguish RIP from RIL. In RIL, the resin is added to the ore at the same time leaching agents are also added. In RIP, the resin is contacted to the leaching effluent and introduced into the circuit after the leaching stage. There are some similar principles but also fundamental differences between the two processes.
Nickel recovery processes from resin-based sulfur solutions are similar to each other and involve stages of charging (loading), elution and regeneration. Thus, resins can be used to treat clarified solutions (through RIS—resin in solution), for pulps (through RIP—resin in pulp) or resin in leach (RIL). From a practical standpoint, a major difference is mechanical resin resistance and its adequate grain size (granulometry). This implies differences in vat stirring systems and in pulp-adsorbent separation. A case in point is using air stirring systems (pachuca) for adsorption, rather than mechanically-stirred vats.
Leaching liberates metals from ore through chemical dissolution. It is the basis for most hydrometallurgical extraction processes. Leaching's chief objective is to selectively liberate a maximum amount of the metal of interest. Since acid leaching procedures for nickel are normally aggressive, impurities are also liberated along with the metals of interest in solution. Leaching is a well-established successful method of mineral extraction, especially for high-grade ores. In contrast, leaching low-grade ores is costly and economically unfeasible, given a high acid consumption yielding low concentration of metals of interest, if compared to the presence of impurities. This implies processing large volumes of diluted solutions in per-unit purification operations, in order to obtain a pure and concentrated solution of the metal of interest, conducive to its final recovery. In some cases, leaching and transfer of species of interest become very difficult, depending of the concentration of these metals in solution, as per Lê Chatelier's Law. In order to avoid this phenomenon, multi-stage leaching circuits are used, preferably operating in countercurrent flow with the presence of resins.
Nickel recovery can be done through resin in leach as proposed in the present invention. Metals such as copper, iron and aluminum easily dissolve in the acid solution. Under conditions necessary to nickel dissolution, acid will react with these metals and be consumed. Ionic exchange resins can be used to recover little-soluble ores or ores bearing solid particles hard to dissociate and form ion traces in solutions. Dissolution balance is established between ions dissolved in solution and solid particles. If the traces of dissolved ions are removed from the solution through ionic exchange, the balance is displaced and further dissolution soon occurs, as per Lê Chatelier's Law. It is essential for the economics of the process that the ionic exchange resin have high selectivity and high charging (loading) balance for the species of interest with low concentrations in the solution. Full dissolution of partially-soluble solids and total liberation of the species of interest are possible, if enough resin is present. Recovery of such species can also be improved, if the contaminant species are removed from the solution during leaching (via precipitation methods).
Nickel concentration in solution increases significantly during leaching. Regrettably, impurity concentration increases simultaneously and, according to Lê Chatelier's Law, excessive increase of species concentration in solution displaces the reaction balance, forming precipitated solids. In order to minimize this reprecipitation reaction, further leaching agent (acid) is necessary to resolubilize nickel, resulting in high acid consumption per mass unit of leached nickel increasing the process' operating cost. The existing balance between solid and dissolved ions is disturbed when the rich solution is removed from between the different leaching stages. Additional solid dissolution then occurs, according to Lê Chatelier's Law.
Given such constraint, it is of the utmost importance to develop a technology capable of providing a more selective extraction process for the species of interest and of minimizing the size of purification and refine units. Moreover, the species of interest must be concentrated in a stage conducive to their easy separation from the leached ore's pulp. Likewise, it is of the most importance to minimize reagent consumption, especially by ganga minerals present in the ore.
Ionic exchange is one of the more promising new technologies available to treat low grade ores. Even though the benefits of this technology in the extractive industry have long been recognized, its progress has been hampered by the unavailability of resins with controlled properties, such as capacity, selectivity and stability. Currently, it is possible to synthesize chemically and physically stable highly-selective resins. This allows ionic exchange resins to be used in hydrometallurgical processes, such as extraction of primary ores, metal recovery in recycled materials, and contaminant removal in effluent treatment.
In the present invention, effluent treatment and operating costs (minimum leaching consumption) is minimized since dissolution (leaching) occurs simultaneously with adsorption (liquid phase removal) of nickel species in a separate stage, with the use of ionic exchange resins. Species of metal of interest with little dissociation are recovered from low-solubility solids using ionic exchange resins in a pulp mix (known as resin-in-leach mix) simultaneously containing the ore and the resin. Traces of ions rendered soluble from the metal of interest are removed from the solution by the resin. This disturbs the balance in the solid/liquid dissociation. Additional solid dissolution thus becomes necessary (Lê Chatelier's Law) to restore the balance concentration of nickel species in solution, which are again removed by reacting in the exchange with the resin. Full solid dissolution and total liberation of the species of interest occurs through continuous displacement of the solid/liquid balance, resulting from the addition of excessive resin. Balance displacement is clearly the main mechanism to recover metal species from little-soluble solids in resin-in-leach mixtures.
Dissociation balance exists between ions dissolved in solution and solid ore particles. This balance is disturbed when metals in this solution, at different leaching stages, are removed. The solution is then restabilized through subsequent solid dissolution, as per Lê Chatelier's Law. Soluble species of interest can be recovered using ionic exchange resins in a pulp mix containing ore and resin (both solid) via RIL. The metal of interest is removed from the solution by the ionic exchange reaction, thus disturbing the solid/liquid dissociation balance. Subsequent solid dissolution occurs and restores the balance concentration of the metal in solution, which is removed again from the solution through ionic exchange reaction. Changing balance conditions is the chief mechanism to recover species in the RIL process.
In principle, ionic exchange is a process governed by electrostatic interactions among different species and occurring between the resin's interior and the external solution. In order to ensure electric neutrality in both phases, the ionic exchange reaction must transfer an equivalent amount of stoichiometric species similarly loaded (charged).
Literature describes different approaches for solving the problems the present invention aims to circumvent.
U.S. Pat. No. 3,998,924 “Recovery of Non-ferrous Metals from Acidic Liquors with a Chelate Exchange Resin in Presence of Iron (III)” to K. Jones, et al. discloses a RIP process comprising contacting (1) an acidic hydrometallurgical leach liquor containing ferric iron and non-ferrous transition metal values at a pH of about 1.0-5.0 with (2) a water-insoluble 2-picolylamine chelate resin in the presence of (3) at least about 0.3 mole per mole ferric iron of a water-soluble reducing agent to concurrently reduce the ferric iron and extract the non-ferrous transition metal values; and thereafter regenerating the loaded chelate resin to recover an enriched aqueous product containing at least 20 parts non-ferrous transition metal per part iron.
GB 2291870A “Recovering Nickel from a Nickel Sulphide Concentrate” to T. Tunley discloses a RIP process for producing ferronickel wherein a solution of nickel sulphate and iron sulphate is produced by leaching a nickel sulphide concentrate. The solution is subjected to an ion exchange step whereafter ferronickel is electronwon from an eluate solution of nickel. The essential steps of said process include: leaching the slurry concentrate containing nickel sulphide, treating the sulphate solution thus formed with solvent extraction or with nickel or ferrous iron selective ion exchange reagent, whereby the nickel is separated from iron as an eluate solution, which is then electrowon to produce ferronickel.
U.S. Pat. No. 5,785,736 “Gold Recovery from Refractory Carbonaceous Ores by Pressure Oxidation, Thiosulfate Leaching and Resin-in-Pulp Adsorption” to K. Thomas et al. discloses a RIP process for treatment of precious metal ores in which gold is leached from an oxidized ore slurry using a thiosulfate salt lixiviant and copper catalyst. Gold and copper are subsequently loaded onto an ion exchange resin. Copper is recovered from the resin by elution with a thiosulfate solution; gold is recovered from the resin by elution with a thiocyanate solution. Gold is recovered from the eluate by precipitation, electrowinning or cementation.
U.S. Pat. No. 6,350,420 “Resin-in-Pulp Method for Recovery of Nickel and Cobalt” to W. Duyvesteyn, et al. relates to the hydrometallurgical processing of nickeliferous or cobaltiferous ores and, in particular, to the direct recovery of nickel and cobalt from a laterite leach slurry by extraction with ion exchange resin, which is then physically separated from the leach slurry. Although said document briefly recites the previous use of resin-in-leach processes for other ores, the subject-matter and the corresponding disclosure are restricted to a RIP process, wherein a relatively coarse ion exchange resin is added to the leach slurry, which contains ore particles much smaller than the ion exchange resin beads. The desired metal(s) are extracted onto the resin and then the resin is separated from the depleted leach slurry by screening or other suitable techniques. Therefore, said document provides a RIP process for metal recovery from acid laterite leach slurry. Although such process also eliminates the costly CCD circuit and provides selective extraction of nickel and cobalt from laterite ores, as in the preset invention, it is not a RIL process and therefore does not provides RIL's advantages recited above.
The WO 07/087,698 “Hybrid Process Using Ion Exchange Resins in the Selective Recovery of Nickel and Cobalt from Leaching Effluents” (co-invented by the present inventor) discloses a process comprising the steps of processing (1) laterite ore (M), being later treated for leaching (2) (atmospheric or pressurized) and including the option of treating the solution from the solid-liquid separation in existing plants (2), said process being characterized by including a cationic or chelating resin hybrid circuit, the first step (3) of ion exchange with resins exhibiting specific selectivity conditions for the removal of iron, aluminum and copper and the increase of the pH, and the second step (4) of ion exchange with resins making it possible to remove nickel and cobalt.
Other documents describing the state of the art include:
1. The Use of Ion-Exchange Resins for the Recovery of Valuable Species from Slurries of Sparingly Soluble Solids—Minerals Engineering, Volume 10, Issue 9, September 1997, Pages 929-945, P. G. R. De Villiersa, J. S. J. Van Deventerb and L. Lorenzenb.
2. Modification and Preparation of Polymeric Adsorbents for Precious-Metal Extraction in Hydrometallurgical Processes—Reactive and Functional Polymers, Volume 36, Issue 2, March 1998, Pages 149-165, J. L. Cortina, E. Meinhardt, O. Roijals and V. Marti.
3. “Chlorine Leaching of Gold-Bearing Sulphide Concentrate and its Calcine—Hydrometallurgy, Volume 29, Issues 1-3, June 1992, Pages 205-215, Li Ximing, Ke Jiajun, Meng Xinhui and Li Bin.
4. “Treatment of Carbonaceous Refractory Gold Ores—Minerals Engineering, Volume 4, Issues 7-11, 1991, Pages 1043-1055, P. M. Afenya.